Anyone who is new to protective coatings has probably felt like they’re reading in a foreign language, studying without comprehending.

Contributors galore have attempted to shorten the learning curve, but the millions of words published in articles introducing protective coatings usually amount to unhelpful regurgitations of the definitions of common resin types.

What use are definitions without a plain-language primer on their underlying concepts?

Let’s begin at the beginning: Why do we use protective coatings? What are they made of? How do they work?

Why do we protect structures with coatings?

The things we build are only worth their construction cost if they last. Unfortunately, those things are exposed to conditions that do not promote their longevity. It doesn’t help that the materials used to construct them are actively trying to disassemble themselves: Unprotected steel corrodes as it strives to turn back into iron, carbon, and other alloying elements. Unprotected concrete crumbles to become the pile of aggregate, binder, and additives that comprise it.

These processes are impossible to stop, and the characteristics of those processes vary based on the conditions in which a structure is located. But protective coatings are designed to slow them down. Their composition varies because chemists have learned that different “recipes” perform better than others, again depending on service conditions.

The breakdown of steel or concrete is inevitable. The goal of a protective coating is to protect a material long enough for it to serve its purpose before the structure is demolished, the materials recycled, and the process starts over.

As an aside, aesthetics sometimes matter. In certain circumstances it’s nice to protect a structure while also making it pretty to look at—think of your hometown’s water tower, for example—but color is almost never the primary concern.

Resins are the backbone of protective coatings

Protective coatings are usually described according to the resin technologies on which they are based.

But even though millions of words have been written on basic introductions to resin types, those resources almost always neglect to include a corresponding introduction to resins generally.

In the coatings industry, resins are molecules that link together to form a barrier. Different coating types rely on different chemical reactions for these barriers to form, but the resulting film shields an underlying surface from its environment.

Resins are either organic or inorganic. Carbon-based organic resins are usually derived from petrochemical sources. Inorganic resins are made from materials other than carbon, such as mined metals or minerals.

Organic and inorganic resins have different advantages and drawbacks depending on a structure’s function, location, and exposures. Some coating systems consist of all organic products. Some are all inorganic. Some use both, an attempt to have the best of both worlds.

What else is in a protective coating?

Besides resin, protective coatings contain a variety of additional substances all vital to their performance:

Solvents like mineral spirits, alcohol, or water keep resins and other coating components suspended prior to application. Once a coating is applied, solvents evaporate in the curing process. The term “volatile organic compounds” (VOCs) refers to these evaporated emissions if the solvent is organic, such as alcohol. Water is not a VOC because its evaporation has no detrimental impact.

Binders are what they sound like: additives incorporated into a coating formula to help hold the film together after it cures. Binders strengthen a resin’s polymer links or fill in gaps between those links to improve a coating’s physical properties and performance.

Hardeners are additives that initiate or aid in the chemical reaction that results in the formation of a resin’s linked polymers (called crosslinking). The amount and nature of a hardener within a coating formula can influence how quickly the crosslinking occurs.

Fillers are inert materials added to a coating formula for improved toughness, durability, thickness, or impermeability.

Pigments are responsible for the color of a coating, but sometimes they also contribute to physical performance. For one example, aluminum pigments in certain coating formulas improve their barrier performance and reflect radiation. For another, zinc dust added to primers results in the formation of a protective surface patina that promotes a very long, low-maintenance service life. In these cases, the pigments’ colors are unimportant.

Biocides are sometimes added to coating formulas to make a coated surface inhospitable to organisms that ordinarily thrive by attaching themselves to it. The most common examples of coatings containing biocides are antifouling coatings applied to the hulls of ships and antimicrobial topcoats applied to floors and walls, such as in food processing facilities.

Understanding curing and adhesion

Liquid coatings come in pails, buckets, or drums, and they’re sprayed, rolled, or brushed onto a surface. Then they dry.

But “dry” is too simple a word to describe a coating’s transition from a free-flowing liquid to a solid barrier that sticks to itself and a surface. That’s why the industry uses the term “cure,” and here’s how it happens:

Solvent evaporation. When the solvent that suspends a coating’s solid contents evaporates, a dry film is left behind. As we noted above, sometimes those solvents are volatile compounds like mineral spirits or alcohol. Sometimes it’s just water. How quickly a solvent evaporates is sometimes important in the context of applying protective coatings. Volatile solvents evaporate faster because the transition temperature from liquid to gas is comparatively low; water-borne coatings usually cure more slowly because water’s transition temperature is comparatively high.

Crosslinking. A protective coating’s film forms when smaller molecules link together, creating thousands of layers of long, densely packed molecule chains. For coating types referred to as single-component, the crosslinking mechanism begins when the material is applied to a surface and exposed to open air. Other types, known as two-component coatings, crosslink when a part A and a part B are mixed. In these types, the coating only cures properly and performs as intended when the parts are mixed according to proper ratios.

Adhesion. The bonds that form during the curing process also contribute to a coating’s adhesion to the surface. But coating chemistry is not the only factor influencing this characteristic. The profile and cleanliness of a surface have just as much to do with it. Profile refers to the available surface area for a coating to cling to, a condition that is measured in microscopic peaks and valleys. Cleanliness refers to the presence or absence of any contaminants that might interfere with a coating’s adhesion to a surface.

A marathon, not a sprint

Protective coatings are not something that can be understood in one sitting.

And yet millions of people who are not experts are daunted at the prospect of making corrosion protection decisions.

The CarboNext education and networking program can help make those decisions a little easier by providing accessible learning materials for professionals new to coatings and connecting them with other professionals with similar challenges or objectives.

It’s a marathon, not a sprint, and every marathon runner will say the same thing: It isn’t possible without training.